An apparatus for intermittently bonding sheet-type workpieces is shown in German Application No. DE G 69 41 387. One of the workpieces has an adhesive on one side thereof and is placed with the adhesive against the other workpiece. The two workpieces are carried between two conveyor belts and through heated pressing plates. The bonded workpieces are then moved into a discharge station on a lower conveyor belt.
German Patent No. DE 2648724 C2 shows a continuous workpiece bonding apparatus. The workpieces are superimposed on one another and fed between two conveyor belts through a heating zone. The heating zone has heated plates mounted adjacent to the moving workpieces. The heated workpieces are passed through a pair of pressing rolls which presses the workpieces together. The bonded workpieces are then moved into a delivery station where they are passed through a cooling zone.
Bonding apparatus such as those described above, may be employed, for example, for bonding materials for making garments and for bonding other types of materials supplied in rolls. German Application No. DE-AS 1504342 shows an example of such bonding apparatus.
One type of adhesive used for bonding sheet-type workpieces are fusion adhesives which are ordinarily provided in liquid, film or powder form. The fusion adhesives are usually applied to the bonding side of one of the workpieces before the workpieces are placed together.
One problem associated with known sheet-type workpiece bonding apparatus is uniformly transferring heat to the workpieces to be bonded. If the apparatus moves the workpieces through a heating and pressing zone, it is desirable for the heat to be transferred uniformly to the workpieces. If the workpieces are not uniformly heated, the fusion adhesive will likely not develop a uniform bond. The layer of fusion adhesive should be heated above at least a threshold temperature throughout the layer to achieve adequate bonding strength. Therefore, if the workpieces are not uniformly heated, but, for example, are insufficiently heated in certain areas, the workpieces likely will not be adequately bonded.
Another problem associated with known sheet-type workpiece bonding apparatus is uniformly and rapidly cooling the workpieces after performing a heating and pressing operation. Rapid cooling of, and controlled removal of thermal energy from the bonded workpieces is necessary to quickly initiate the crystallization process of the fusion adhesive, and to obtain a uniform crystal structure in the resolidified adhesive. Control over the cooling process is critical because the strength of the bond formed by the fusion adhesive may depend substantially in part on the degree of uniformity of its crystal structure developed during the cooling and solidification process. Generally, the strength of the adhesive bond increases with the degree of uniformity in the crystal structure of the resolidified adhesive.
Until now, known sheet-type workpiece bonding apparatus have generally not satisfactorily provided a means for uniformly heating sheet-type workpieces to be bonded together, nor have they provided a satisfactory means for rapidly and uniformly cooling sheet-type workpieces following a heating and pressing operation. These problems are especially critical, for example, in processing garment parts. In making garments, a "sandwich" process is frequently employed, where, for example, two interlinings and two top cloth parts are superimposed on one another into a four-ply stack with fusion adhesive applied between the adjacent plies. The four-ply stack is then moved, for example, by conveyor belts through a heating and pressing zone. If the four-ply stack is not uniformly heated, or, likewise, if after heating and pressing it is not uniformly and rapidly cooled, the fusion adhesive between the stacks likely will not develop uniform bonds. As a result, the durability and strength of the laminated material will be lessened and, thus, the laminated material will likely make a poor quality garment.
Therefore, it is an object of the present invention to overcome the problems and drawbacks of known sheet-type workpiece bonding methods and apparatus.